The present invention relates to a method for producing parts of an antiadhesive organic material in powder form, preferably polyfluorocarbon, and most preferred polytetrafluoroethylene. The invention also relates to parts produced according to the inventive method and also to a device for performing such a method, wherein the device comprises a housing having a receiving chamber and a support for the antiadhesive organic powder material to be treated therein. At least one energy source and at least one electrode are positioned in the receiving chamber. At least one inlet line for a process gas opens into the receiving chamber.
An antiadhesive organic material is, for example, polytetrafluoroethylene. It is a thermally and chemically highly stable thermoplastic material with antiadhesive properties. These properties prevent the polytetrafluoroethylene from becoming directly bonded to other materials. Accordingly, for polytetrafluoroethylene composites a fixed bonding between embedded fillers and the matrix of polytetrafluoroethylene is not possible.
Polytetrafluoroethylene composites containing fibers are characterized in that the fibers have no or only minimal adhesion to the polytetrafluoroethylene due to the antiadhesive properties of the polytetrafluoroethylene. Because of an inner notching effect of the fibers within the composite, the fibers are known to considerably reduce the stability of the composite material.
For elastomer-modified polytetrafluoroethylene (EMP) there is also no fixed or secure bonding possible between the embedded powder particles of polytetrafluoroethylene and the elastomer matrix. This is especially disadvantageous when the EMP is subjected to tensile load and exposed to various (aggressive) media. In these cases, the polytetrafluoroethylene particles cannot contribute to the force distribution because they have no adhesive connection to the elastomer matrix. The forces therefore can only be transmitted by the very thin matrix stays of elastomer material between the polytetrafluoroethylene particles. Especially when a high amount of polytetrafluoroethylene (PTFE) filler is embedded in the elastomer matrix, i.e., for an amount of approximately 20 to 50% by weight PTFE in the matrix, the intermediate elastomer regions are very sensitive and can be quickly destroyed when exposed to (aggressive) media or high temperature.
It is therefore an object of the present invention to embody the aforementioned method, the aforementioned part, and the aforementioned device such that the organic powders that have antiadhesive properties can be imparted in a simple and inexpensive manner with properties allowing a fixed bonding between same particles or with other materials.
This object is inventively solved for the method in that the antiadhesive organic powder is plasma-treated before further processing for manufacturing the parts occurs. The parts of the present invention are characterized in that a plasma-treated antiadhesive organic powder is used for the parts. The inventive device is characterized in that a rotary drum is used as a support for the antiadhesive organic powders.
The plasma treatment of the antiadhesive organic powder materials results in a plasma etching and/or in chemical changes in the micro-range at the surface of the powder particles. The plasma-activated surface of the powder particles ensures that these particles can reliably fixedly bond to one another or with other components without requiring wet-chemical etching processes. For a polytetrafluoroethylene fiber composite, the fibers are embedded fixedly in the polytetrafluoroethylene matrix so that the stability of such a fiber-filled polytetrafluoroethylene composite is considerably increased. At the same time, an increase of the composite material stiffness occurs. The undesirable cold flowing properties and creeping of polytetrafluoroethylene can be substantially decreased in this manner. For elastomer-modified polytetrafluoroethylene (EMP) a fixed adhesion between the polytetrafluoroethylene particles and the elastomer matrix occurs. Because of this fixed adhesion the total boundary surface can receive and distribute forces. The polytetrafluoroethylene particles thus contribute to the force flow within the composite material so that the entire composite material exhibits only minimal sensitivity. The term powder in the context of the present invention also includes micro-powders which are treated in the same manner as disclosed above by a plasma treatment. Carrying out the plasma activation of the powder or micro-powder in the rotary drum of the inventive device ensures an excellent mixing of the powder during the plasma treatment so that an optimal activation of the powder particles is realized.